MPI_Op_create

Creates a user-defined combination function handle

Synopsis

#ifdef ENABLE_QMPI
#ifndef MPICH_MPI_FROM_PMPI
int QMPI_Op_create(QMPI_Context context, int tool_id, MPI_User_function *user_fn, int commute,
                   MPI_Op *op) MPICH_API_PUBLIC

Input Parameters

user_fn
user defined function (function)
commute
true if commutative; false otherwise. (logical)

Output Parameters

op
operation (handle)

Notes on the user function

The calling list for the user function type is 
    typedef void (MPI_User_function) (void * a,
                  void * b, int * len, MPI_Datatype *);
where the operation is b[i] = a[i] op b[i], for i=0,...,len-1. A pointer to the datatype given to the MPI collective computation routine (i.e., MPI_Reduce, MPI_Allreduce, MPI_Scan, or MPI_Reduce_scatter) is also passed to the user-specified routine.

Notes on collective operations

The reduction functions (MPI_Op) do not return an error value. As a result, if the functions detect an error, all they can do is either call MPI_Abort or silently skip the problem. Thus, if you change the error handler from MPI_ERRORS_ARE_FATAL to something else, for example, MPI_ERRORS_RETURN, then no error may be indicated.

The reason for this is the performance problems in ensuring that all collective routines return the same error value.

Thread and Interrupt Safety

This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as malloc or other non-MPICH runtime routines that are themselves not interrupt-safe.

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.

Errors

All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

MPI_SUCCESS
No error; MPI routine completed successfully.

MPI_ERR_ARG
Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).
MPI_ERR_OTHER
Other error; use MPI_Error_string to get more information about this error code.

See Also

MPI_Op_free